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House Electrical Circuit

05/31/2021 4:29 PM

Hey guys and gals.

Sorry for the long post. A lot going on.

My wife and I purchased our 50 year old home 2 years ago. I had an inspection done which as I expected, suggested a replacement of the electric panel. I had the panel replaced.

Recently, I set my wife up in a spare bedroom for her to use as an office. She told me she was experiencing slight electrical shocks through the computer keyboard. I checked the circuit and plugged in an a tester and it showed that there was reversed polarity. I removed the outlet and, yes, the black and white wires were reversed.

I removed the outlet and replaced the wires correctly. I again used the plugin circuit tester and it now indicates that there is an open ground.

Also, to de-energize the circuit, I closed ALL of the 120V breakers and, the circuit was still live. Then, thinking that someone had tapped into a 240v circuit, turned off all of the 240v breakers. The 120v circuit was still live. I had to turn off the main breaker to kill the circuit.

Ideas??

Thanks,

Don

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#1

Re: House electrical circuit

05/31/2021 4:52 PM

So it's not uncommon to tap into the main with a second subpanel, I suspect that is what you have...that is allowed, even up to three times I think...Look for additional wires coming off the incomers...the subpanel should be close by....

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#2
In reply to #1

Re: House electrical circuit

05/31/2021 5:35 PM

Thanks. There is a 240v sub panel in my detached garage, 50 feet away. But, even with that circuit off, I am still getting power on the offending 120v circuit even when I turn off all of the breakers, the power is still on to that one circuit. I'm not sure where to go from here.

I can install panels, wire circuits, etc, but this has me really confused.

Thanks again.

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#3
In reply to #2

Re: House electrical circuit

05/31/2021 5:47 PM

There could be a separate circuit feeding off the lower lugs of the main breaker...in any case you have another subpanel someplace and you'll need to run a separate ground wire if none exists...I would trace the live wire back from the outlet with a non-contact voltage detector....

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#5
In reply to #2

Re: House electrical circuit

05/31/2021 8:05 PM

Maybe a breaker that is not really opening?

Plug in a lamp or some other load into the outlet, get a clamp-on ammeter and see if any hot wires in the breaker box have any current.

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#7
In reply to #5

Re: House electrical circuit

05/31/2021 10:02 PM

Here is even a better idea. They have this gizmo that transmits a signal that you plug into an outlet. A receiver that comes with it allows you to trace what breaker feeds that outlet.

https://www.homedepot.com/p/Klein-Tools-Digital-Circuit-Breaker-Finder-ET300/202330830?MERCH=REC-_-pipsem-_-308709729-_-202330830-_-N&

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#9
In reply to #5

Re: House electrical circuit

05/31/2021 11:28 PM

Breakers generally fail in the open position, can't remember ever seeing one fail in the closed position...easy enough to check with a multimeter, just check each breaker to common...

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#12
In reply to #9

Re: House electrical circuit

06/01/2021 9:42 AM

True that they NORMALLY fail open, but in over 50 years of doing electric work I have seen more than my share of breakers failing closed. (One of the reasons for PPE when doing any electric work) Using a meter at the panel AND at the receptical will tell if it is getting power from another source. A non contact test will tell of another problem. Is the receptical hot and producing the voltage source or is something else hot and the rec is providing the ground path? Also, just testing line to neutral just tells if the circuit should work, it does not tell if it will kill you. Test to ground, too. an open neutral may not register at the rec, but it is still hot. Not common problems but DEADLY. There are times when DIYers need to throw in the towel and get a trained pro. JHF

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#13
In reply to #12

Re: House electrical circuit

06/01/2021 11:43 AM

The neutral is connected to the ground, if it wasn't nothing would be working except the 240v circuits....I've never seen a residential breaker that would open normally and remain closed in the breaker itself...I've seen breakers that wouldn't open for whatever reason, but that's an obvious problem...These circuits are working he just lacks a separate ground to this receptacle, not uncommon in older houses...the polarity doesn't matter as far as most circuits working, it's more of a safety factor that was adopted some time ago, the polarized plug....years ago it didn't matter which wire went to which side of the plug....now we have the grounded polarized plug and GFCI receptacles...

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#14
In reply to #13

Re: House electrical circuit

06/01/2021 12:18 PM

I was doing electric work in LA in the 60's and 70's. The early 70's is when they started requiring ground wires and 3 wire devices. There is something odd going on that needs more testing than can be covered in this forum. There is a degree of danger so I still say a trained, exerienced person with proper test equipment and PPE is needed to be sure the circuit is correct and safe. -- JHF

P.S. I have seen several breakers that failed in the closed position but with the handle in the open position. For safety sake, do not rule anything out until it is proved safe. I have also seen many sub panels with no ground, neutral only and the ground floating or bonded to the neutral.

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#11
In reply to #1

Re: House electrical circuit

06/01/2021 7:03 AM

My sub panel is being fed by a 240v breaker in the main panel. I'll check the sub panel today to see if the grounds and neutral bar are correct.

Thanks.

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#4

Re: House electrical circuit

05/31/2021 6:11 PM

I removed the outlet and replaced the wires correctly. I again used the plugin circuit tester and it now indicates that there is an open ground.

The voltage tester has three lights, indicating voltage (and continuity) between hot-neutral (HN), hot-ground (HG), and ground-neutral (GN).

Correct wiring should light HN and HG. Current from hot returns through both neutral and through ground, which is connected to neutral somewhere.

If hot and neutral are reversed, HN and GN will light, current flowing from the neutral of the socket back through ground and the hot side of the outlet.

If the ground is open, current will not return through ground in either of the above situations.

Here's my wild guess: The ground wire was not fastened securely and when you were correcting the hot-neutral swap, the ground wire came loose.

You really should get an electrician to check all the wiring. It's not uncommon in an old house for someone, sometime, to have miswired something.

http://thecircuitdetective.com/outlet_tester_readings.php

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#6

Re: House Electrical Circuit

05/31/2021 8:46 PM

As far as the circuit that remains hot, my WAG is you have a failed breaker that won't open. The other possibility that comes to my mind is that circuit is being back fed from another path with the identical split phase. Both scenarios require working HOT to repair. Proper PPE and isolated tools are recommended.

As for the occasional shocks from the computer, most computers today are double insulated so a person does not touch any potentially conductive surfaces. The power supply isolation in that computer is failing. All of the external, metallic chassis parts should be bonded through that power supply to the ground pin. A swapping of Hot and Neutral will not change this. You might have something else that is Hot and the grounds of the computer provide a return path. Possibly static discharges are responsible.

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#8

Re: House Electrical Circuit

05/31/2021 10:41 PM

I'd agree that a 'hung' breaker would be a good place to start; just use a VOM at the panel(s) & probe each breaker's output with all of them turned off, looking for a hot wire.

BTW, we understand that you meant that you turned the breakers off, but the correct term is 'opened'; not 'closed'. 'Closed' indicates that you have completed the circuit (turned the switch/breaker/etc ON), in electrical jargon.

Charlie

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#10

Re: House Electrical Circuit

06/01/2021 6:10 AM

How are you testing the outlet?If using a digital meter,they can read the very slightest leakage current,even capacitance or inductance from nearby conductors.

Plug in a load to the receptacle,then test the other half of the receptacle.

The load should remove any residual voltage.

Check that the sub panel does not have the bonding strap(Neutral to equipment ground) attached.

Sub panels must not have the bonding strap,and all equipment grounds should be insulated from neutral at the panel.This prevents a difference in potential of the two panels grounds.

Reference:

https://www.mikeholt.com/forum/Forum1/HTML/003455.html

Also see article 250 of the NEC.

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#15

Re: House Electrical Circuit

06/01/2021 1:25 PM

Since keyboards are plastic, she was probably getting static discharges. You will want to check all neutral and ground wires screws to see if they are tight. As for the live wire, look for a wire bypassing a breaker.

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#16
In reply to #15

Re: House Electrical Circuit

06/01/2021 2:27 PM

Could be static discharge...if the humidity is very low....they do make anti-static kits...cheaper just to spritzer ever so often...A damp surface kills static...

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#17

Re: House Electrical Circuit

06/01/2021 2:34 PM

First of all, thanks for all of the advice.

I checked my sub panel in my detached workshop which is about 50 ft from the house and main panel. The sub panel has one common ground and neutral bar. All of the ground and neutral wires are connected to the same bar. No ground rod by the shop.

Also, there are four 120v breakers and one 60 amp, 240v breaker. I think the 60 amp breaker was overkill. It was installed to service an icemaker for the previous owner. I've had it turned off since I moved in. But, in addition to the wire servicing the disconnected icemaker, there are wires connected to the same breaker going to a 240v clothes dryer outlet also not in use.

As I relayed previously, I had a home inspection prior to buying the home. And, I had the main panel replaced by an electrician per our local regulations. The electrician inspected the sub panel said all was ok.

Should I install a 2nd bar to isolate the neutral and ground wires? And can I use the 240v 60 amp breaker to run to another sub panel on the other side of the shop to service my table saw and RV outlet? There are not enough breakers in the existing sub panel to service everything.

Thanks.

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#18
In reply to #17

Re: House Electrical Circuit

06/01/2021 11:20 PM

I would separate the grd and neutral and install a ground rod near the panel...yes you can add another subpanel from the 60 amp breaker....or you can just replace the distribution box you have now with a bigger one.....

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#19

Re: House Electrical Circuit

06/02/2021 4:54 AM

How many sockets are in that "spare" room? Is the one the computer uses the only one that remains live when all breakers are off?

I wonder if a previous occupant had some kind of medical equipment that had to remain on at all times.

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#20
In reply to #19

Re: House Electrical Circuit

06/02/2021 11:50 PM

It would still have a breaker....usually red and marked for purpose...

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#21

Re: House Electrical Circuit

06/10/2021 4:32 PM

From the above, where WAG seems to be going on, the best approach would be to consult a qualified local Electrician.

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